1. Field of the Invention
The present invention relates to a braiding yarn made of expanded graphite which is suitable for a gland packing that is to be used in a shaft seal part of a fluid apparatus or the like, and also to such a gland packing.
2. Description of Related Art
Conventionally, a braiding yarn made of expanded graphite has been proposed in which plural expanded graphite tapes having a predetermined width are stacked to constitute an expanded graphite base member, and the outer periphery of the expanded graphite base member is externally reinforced by knitting or tubular-plain-stitching reinforcing wire members such as stainless steel wires (for example, see Japanese Patent Application Laying-Open No. 6-17937).
In the braiding yarn made of expanded graphite having this configuration, the outer periphery of the expanded graphite base member is covered by, for example, knitting reinforcing wire members such as stainless steel wires. During a process of braiding plural yarns to produce a gland packing, therefore, the knit of the reinforcing wire members sufficiently resists tensile and torsional forces produced in each of the yarns, whereby the expanded graphite base member in the knit is prevented from being broken.
However, the braiding yarn made of expanded graphite in which the outer surface of the expanded graphite base member is covered by knitting or tubular-plain-stitching reinforcing wire members such as stainless steel wires has a problem in that the process of covering the expanded graphite base member with knitting or tubular-plain-stitching the reinforcing wire members requires a long time period and hence the productivity is poor.
The inventor thought up a configuration in which an expanded graphite base member is externally reinforced by spirally winding a reinforcing wire member therearound.
However, it was found that, when such a braiding yarn made of expanded graphite is bent with a small radius of curvature, the reinforcing wire member on the inner peripheral side of the bent portion slacks, and the reinforcing wire member separates and protrudes from the outer face of the expanded graphite base member on the inner peripheral side of the bent portion.
In the case where the counter member is, for example, a rotation shaft, when such slack once occurs, the slack is repeatedly bent in the forward and reverse rotational directions of the rotation shaft in accordance with forward and reverse rotations of the rotation shaft. When time elapses, there arises a possibility that the basal portion of the slack is broken. When such breakage occurs, a broken surface may damage the counter member. In the case where the counter member is a stem, in accordance with reciprocal motion of the stem, such slack is repeatedly bent in the reciprocal directions, and, when time elapses, there arises a possibility that the basal portion of the slack is broken. When such breakage occurs, a broken surface may damage the counter member.
The invention has been conducted in order to solve the problems. It is an object of the invention to provide a braiding yarn made of expanded graphite in which a reinforcing wire member is spirally wound around an expanded graphite base member, and, even when the braiding yarn is bent with a small radius of curvature, the reinforcing wire member can be surely prevented from slacking on the inner peripheral side of the bent portion, and the sealing property is not impaired, and also a gland packing in which such a braiding yarn made of expanded graphite is used.
In the braiding yarn disclosed in Japanese Patent Application Laying-Open No. 6-17937, most of the outer surface of the expanded graphite base member is covered by the knitted or tubular-plain-stitched reinforcing wire members such as stainless steel wires, and therefore there is a problem in that the adaptability and sealing property with respect to a counter member such as a rotation shaft or a stem (hereinafter, referred to merely as “counter member”) which are characteristics of the expanded graphite base member cannot be sufficiently exerted. As shown in FIG. 16, in a braiding yarn 1, the outer surface of an expanded graphite base member 2 is covered by knitting or tubular-plain-stitching reinforcing wire members 3. As shown in FIG. 15, a plurality of such braiding yarns 1 are braided or twisted to constitute a gland packing G, and the gland packing G is inserted into a packing box A and pressed by a packing gland B. When the braiding yarns 1 of the gland packing G are compressed in the directions C in FIG. 16, the expansion amount by which the expanded graphite base member 2 tends to outward expand between the reinforcing wire members 3 adjacent to each other on the outer surface, as indicated by the broken line e is reduced. Therefore, the contact with a counter member 9 at a sufficient contact pressure and a sufficient contact area becomes insufficient, and the adaptability and sealing property with respect to the counter member 9 are reduced.
The invention has been conducted in order to solve the problems. It is another object of the invention to provide a braiding yarn made of expanded graphite which has sufficient resistance due to external reinforcement against tensile and torsional forces produced in each of yarns during a process of producing a gland packing, and in which the productivity can be enhanced, and the adaptability and sealing property with respect to a counter member can be improved.
It is a further object of the invention to provide a gland packing in which an externally reinforced braiding yarn is used, and in which the adaptability and sealing property with respect to a counter member can be improved.